The 1985 Castrol 500 was an endurance race for "Group A" Touring Cars staged at the Sandown International Motor Racing Circuit in Victoria on 15 September 1985. Race distance was 129 laps of the 3.878 km (1.928 mi) circuit, totaling 500.262 km.
The field was divided into three classes according to engine displacement.Class A : 3001cc to 6000cc
Class B : 2001cc to 3000cc
Class C : Up to 2000cc
The event was Round 3 of both the 1985 Australian Endurance Championship and the 1985 Australian Manufacturers' Championship. There were 36 starters, of whom 18 were classified as finishers.
The race was won by the JPS Team BMW 635 CSi of Australian Touring Car Champion Jim Richards, and his co-driver Tony Longhurst. It was Longhurst's first major win in Australian touring car racing. JPS Team BMW made it a 1-2 finish when their second car, driven by Neville Crichton and on-loan Nissan team driver George Fury finished only a few seconds behind. Finishing in third place was the surprising Toyota Supra of Peter Williamson and 1985 Formula Ford Driver to Europe champion Tomas Mezera.
The 1985 Castrol 500 was the first time since 1972 that neither Peter Brock or Allan Moffat had won the Sandown enduro. 1984 Castrol 500 winner Brock, who claimed pole position with a time of 1:52.3 in his Holden Dealer Team VK Commodore, suffered engine failure after 41 laps, while Moffat, who was without a drive in 1985 due to Mazda not racing in Group A, was part of the ABC television commentary team.
Before his retirement, Brock set the fastest lap of the race with a 1:53.7.
Results are given below.